1 /* Copyright (C) 1991-2023 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contributed by Torbjorn Granlund (tege@sics.se).
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
23 #if defined HAVE_STRING_H || defined _LIBC
30 # define MEMCMP memcmp
38 # if __BYTE_ORDER == __BIG_ENDIAN
39 # define WORDS_BIGENDIAN
42 #else /* Not in the GNU C library. */
44 # include <sys/types.h>
46 /* Type to use for aligned memory operations.
47 This should normally be the biggest type supported by a single load
48 and store. Must be an unsigned type. */
49 # define OPSIZ (sizeof (op_t))
51 /* Type to use for unaligned operations. */
52 typedef unsigned char byte;
54 # ifndef WORDS_BIGENDIAN
55 # define MERGE(w0, sh_1, w1, sh_2) (((w0) >> (sh_1)) | ((w1) << (sh_2)))
57 # define MERGE(w0, sh_1, w1, sh_2) (((w0) << (sh_1)) | ((w1) >> (sh_2)))
60 #endif /* In the GNU C library. */
62 #ifdef WORDS_BIGENDIAN
63 # define CMP_LT_OR_GT(a, b) ((a) > (b) ? 1 : -1)
65 # define CMP_LT_OR_GT(a, b) memcmp_bytes ((a), (b))
68 /* BE VERY CAREFUL IF YOU CHANGE THIS CODE! */
70 /* The strategy of this memcmp is:
72 1. Compare bytes until one of the block pointers is aligned.
74 2. Compare using memcmp_common_alignment or
75 memcmp_not_common_alignment, regarding the alignment of the other
76 block after the initial byte operations. The maximum number of
77 full words (of type op_t) are compared in this way.
79 3. Compare the few remaining bytes. */
81 #ifndef WORDS_BIGENDIAN
82 /* memcmp_bytes -- Compare A and B bytewise in the byte order of the machine.
83 A and B are known to be different.
84 This is needed only on little-endian machines. */
86 static int memcmp_bytes (op_t, op_t) __THROW;
89 memcmp_bytes (op_t a, op_t b)
91 long int srcp1 = (long int) &a;
92 long int srcp2 = (long int) &b;
97 a0 = ((byte *) srcp1)[0];
98 b0 = ((byte *) srcp2)[0];
107 static int memcmp_common_alignment (long, long, size_t) __THROW;
109 /* memcmp_common_alignment -- Compare blocks at SRCP1 and SRCP2 with LEN `op_t'
110 objects (not LEN bytes!). Both SRCP1 and SRCP2 should be aligned for
111 memory operations on `op_t's. */
113 memcmp_common_alignment (long int srcp1, long int srcp2, size_t len)
120 default: /* Avoid warning about uninitialized local variables. */
122 a0 = ((op_t *) srcp1)[0];
123 b0 = ((op_t *) srcp2)[0];
129 a1 = ((op_t *) srcp1)[0];
130 b1 = ((op_t *) srcp2)[0];
136 if (OP_T_THRES <= 3 * OPSIZ && len == 0)
138 a0 = ((op_t *) srcp1)[0];
139 b0 = ((op_t *) srcp2)[0];
142 a1 = ((op_t *) srcp1)[0];
143 b1 = ((op_t *) srcp2)[0];
147 if (OP_T_THRES <= 3 * OPSIZ && len == 0)
154 a0 = ((op_t *) srcp1)[0];
155 b0 = ((op_t *) srcp2)[0];
157 return CMP_LT_OR_GT (a1, b1);
160 a1 = ((op_t *) srcp1)[1];
161 b1 = ((op_t *) srcp2)[1];
163 return CMP_LT_OR_GT (a0, b0);
166 a0 = ((op_t *) srcp1)[2];
167 b0 = ((op_t *) srcp2)[2];
169 return CMP_LT_OR_GT (a1, b1);
172 a1 = ((op_t *) srcp1)[3];
173 b1 = ((op_t *) srcp2)[3];
175 return CMP_LT_OR_GT (a0, b0);
183 /* This is the right position for do0. Please don't move
187 return CMP_LT_OR_GT (a1, b1);
191 static int memcmp_not_common_alignment (long, long, size_t) __THROW;
193 /* memcmp_not_common_alignment -- Compare blocks at SRCP1 and SRCP2 with LEN
194 `op_t' objects (not LEN bytes!). SRCP2 should be aligned for memory
195 operations on `op_t', but SRCP1 *should be unaligned*. */
197 memcmp_not_common_alignment (long int srcp1, long int srcp2, size_t len)
204 /* Calculate how to shift a word read at the memory operation
205 aligned srcp1 to make it aligned for comparison. */
207 shl = 8 * (srcp1 % OPSIZ);
208 shr = 8 * OPSIZ - shl;
210 /* Make SRCP1 aligned by rounding it down to the beginning of the `op_t'
211 it points in the middle of. */
216 default: /* Avoid warning about uninitialized local variables. */
218 a1 = ((op_t *) srcp1)[0];
219 a2 = ((op_t *) srcp1)[1];
220 b2 = ((op_t *) srcp2)[0];
226 a0 = ((op_t *) srcp1)[0];
227 a1 = ((op_t *) srcp1)[1];
228 b1 = ((op_t *) srcp2)[0];
233 if (OP_T_THRES <= 3 * OPSIZ && len == 0)
235 a3 = ((op_t *) srcp1)[0];
236 a0 = ((op_t *) srcp1)[1];
237 b0 = ((op_t *) srcp2)[0];
241 a2 = ((op_t *) srcp1)[0];
242 a3 = ((op_t *) srcp1)[1];
243 b3 = ((op_t *) srcp2)[0];
247 if (OP_T_THRES <= 3 * OPSIZ && len == 0)
254 a0 = ((op_t *) srcp1)[0];
255 b0 = ((op_t *) srcp2)[0];
256 x = MERGE(a2, shl, a3, shr);
258 return CMP_LT_OR_GT (x, b3);
261 a1 = ((op_t *) srcp1)[1];
262 b1 = ((op_t *) srcp2)[1];
263 x = MERGE(a3, shl, a0, shr);
265 return CMP_LT_OR_GT (x, b0);
268 a2 = ((op_t *) srcp1)[2];
269 b2 = ((op_t *) srcp2)[2];
270 x = MERGE(a0, shl, a1, shr);
272 return CMP_LT_OR_GT (x, b1);
275 a3 = ((op_t *) srcp1)[3];
276 b3 = ((op_t *) srcp2)[3];
277 x = MERGE(a1, shl, a2, shr);
279 return CMP_LT_OR_GT (x, b2);
287 /* This is the right position for do0. Please don't move
290 x = MERGE(a2, shl, a3, shr);
292 return CMP_LT_OR_GT (x, b3);
297 MEMCMP (const void *s1, const void *s2, size_t len)
301 long int srcp1 = (long int) s1;
302 long int srcp2 = (long int) s2;
305 if (len >= OP_T_THRES)
307 /* There are at least some bytes to compare. No need to test
308 for LEN == 0 in this alignment loop. */
309 while (srcp2 % OPSIZ != 0)
311 a0 = ((byte *) srcp1)[0];
312 b0 = ((byte *) srcp2)[0];
321 /* SRCP2 is now aligned for memory operations on `op_t'.
322 SRCP1 alignment determines if we can do a simple,
323 aligned compare or need to shuffle bits. */
325 if (srcp1 % OPSIZ == 0)
326 res = memcmp_common_alignment (srcp1, srcp2, len / OPSIZ);
328 res = memcmp_not_common_alignment (srcp1, srcp2, len / OPSIZ);
332 /* Number of bytes remaining in the interval [0..OPSIZ-1]. */
333 srcp1 += len & -OPSIZ;
334 srcp2 += len & -OPSIZ;
338 /* There are just a few bytes to compare. Use byte memory operations. */
341 a0 = ((byte *) srcp1)[0];
342 b0 = ((byte *) srcp2)[0];
353 libc_hidden_builtin_def(memcmp)
356 weak_alias (memcmp, bcmp)
360 strong_alias (memcmp, __memcmpeq)
361 libc_hidden_def(__memcmpeq)